This paper provides a unified approach to study the influence of uncertainty and spillovers on the direction of R&D policy when firms engage in international R&D competition. When the reward to the winner is exogenously given, it is shown that whether a government will tax or subsidize its firm is sensitive to the type of uncertainty that characterizes the R&D process. When the reward to the winner is endogenously determined by R&D spending, the direction of optimal policy is not only sensitive to the type of uncertainty, but also sensitive to the degree of spillovers.